Various techniques for Q-switching a laser have been described in the prior art, including techniques utilizing an acousto-optic Q-switching mechanism, which is spaced apart from the laser medium and aligned with the optical axis of the laser resonator, such that the acousto-optic material responds to electrical excitation by developing an acoustic beam which interacts with the optical beam generated in the laser resonator. The acousto-optic switching mechanism is arranged to prevent the generation of a laser output as long as sufficient optical loss is introduced into the resonator by the presence of an acoustic beam. When the acoustic beam is terminated, the acoustically introduced optical loss is eliminated, and the laser resonator releases its stored energy in a single pulse laser output of typically between 10 and 100 nanoseconds in length. The insertion of an acousto-optic Q-switching mechanism, which is separate and spaced apart from the laser medium, in accordance with the prior art technique, introduces additional optical surfaces through which the laser light must pass thus increasing the power losses encountered in the laser resonator.
The acousto-optic Q-switching mechanism functions as an optical shutter which, in response to RF excitation, appears as a closed shutter preventing the transmission of a laser output and as an open shutter in the absence of RF excitation thus permitting the transmission of a laser output. This laser modulation achieved by conventional acousto-optic Q-switching mechanisms provides a technique for controlling the energy content of the laser output in addition to determining the pattern of laser output pulses developed by the laser resonator.
A detailed discussion and illustration of an acousto-optical Q-switching mechanism positioned in a spaced apart relationship with a laser medium to operate in accordance with the above discussion is present in U.S. Pat. No. 3,746,886, issued July 17, 1973 and U.S. Pat. No. 3,805,196, issued Apr. 16, 1974 both of which are assigned to the assignee of the present invention and incorporated herein by reference.